Sorry for the length but no other way to go...

After being a great cheap ride ($700) my '74, with that oh so loved 18RC motor, has become cranky. In 101 degree heat less than a mile down the road it died, it would start but wouldn't keep running and needed help to limp home-no power, stalling etc.

Did compression test: C1-40dry 60wet C2-80dry 161wet C3-119dry 154wet C4 119dry 162wet. This indicates worn rings right? well hold on

Pulled plugs: choc brown but dry as could be-note that when I got the truck the carb had been badly hacked up, no choke, failed secondary diaphragm, etc. I have a new carb and was bout to install when this went down.

So next I started the teardown believing it was worn rings (not saying it isn't that to some degree), burnt valves, blown head gasket, etc.

Head gasket was fine. So I flipped the head over and poured solvent into the combustion chamber expecting it to drain out (at least in the #1 hole). Nope they are still holding ALL of it 6 hours later check it out.

So the valves are good right? The #4 with highest compression does have some pitting on the E valve and it's piston top has a divet where the intake valve, at some point, hit it but I don't think it was this valve as there is no damage to the valve.

The pistons all have even carbon, the bores have no visible damage or any bad scoring that I can feel, pistons are within .003" all around, they will move a tiny bit with great sideways force but its hardly noticable. There is a small wear ring at the top but within spec.

The truck never smoked much at all, I would have to floor it to see any smoke and that was hard to see even then and no oil consumption. Anyone have any ideas what is going on here? Is there anything that can cause this besides burnt rings? I recently did an oil change. I believe the head has been recon since factory birth and someone has had the motor out of the truck because it's been RTV'd on timing cover and hoisting hooks are missing. Thanks for any advice or ideas.

 

Just because the combustion chambers in the head hold solvent like they are doing doesn't mean those valves aren't leaking when each piston builds pressure. You've already torn it apart, I'd have a good machine shop check the head and at least freshen up the valve seats, seals, and guides. Also need to freshen up the bottom end with new rings and bearings. Make sure you check each cylinder thoroughly for tolerances. At the very least you want to hone them and nice 30 degree crosshatch honing pattern in each cylinder prior to reinstalling pistons with new rings. That's a start. Good luck.

 

Thanks for the reply Gov't Mule. That's not the best news but at least now it makes more sense to me. What your saying is that if the chambers were leaking quickly then the valves are definitely bad, but even holding they might be weak and not properly seating.

I've been trying to find a shop who will work on the head and possibly do a re-bore, but so far they all say 'probably be a total rebuild once we get in there, around $1500-2300!.' That's a no go for me financially and common sense wise since an already rebuilt motor is cheaper-but I can't find an 18R rebuilt and I don't fully understand how to modify the truck to fit a 20R or 22R. So I am back to hoping I can just get the head redone and fit new rings. If I keep the crankshaft parts together and put them back where they were will I need to do anything else or is it likely that will work? I am looking for a gauge to check the tolerances of the bores. Thanks again.

 

If money is an issue could just lap the valves, new rings, put it together and see what happens. Worst case scenario you're out less than 100 bucks: rings, lapping compound, head gasket.

I doubt you're losing that much compression out of valves if they're holding gas like that in my opinion but I don't really know.

Buy http://www.harborfreight.com/hand-to...-set-5649.html and use it with your micrometer to check the bores.

With compression that low I wouldn't be surprised if some of those rings are broken. Can't really tell, but C2 looked like there may have been a vertical line in it. If that's the case new rings should do the trick.

In my opinion I'd pull that bottom end apart. Not too much more work to put that bottom end on an engine stand. You can always just put it back together the same way (minus old rings). Let us know what you find when it's apart. I also took a power washer to mine when it was bare to really clean out all the oil passages and stuff.

Also maybe its possible it jumped a tooth on the timing chain? I don't really know but that seems like it could make sense to me. Measure the chain and see if it's stretched or count the links between the bright links and count how many are between your timing marks.

 

Thanks for ideas ConSeann3ry. I am considering trying to save it by doing the work myself. If I can get a year or two out of $150 or so then it's worth it. Couple of questions:

I found some replacement valves fairly cheap, exhaust and intake (std size) for $40, and I can get the seals for about $16, lapping tool and compound about $16. The only springs I could find were $50. Found some rings that are listed as "STD - ART PISTON WITH .156" DEEP OIL RING GROOVE" for $15.00 a set-so $60.00. By my calculations this is about $150 with tax and shipping maybe a little more. Do you think I should get new valves or just try to lap the existing ones? What about the new springs is that a good idea, and the deep oil rings seem like they might work if the bore is still close to original. I am planning on getting the tool to measure bore either Wed or Thursday.

Don't think it jumped the timing chain because it's sitting at TDC on the pulley, the rotor is pointing at the #1 wire, the cam's sprocket is in TDC position and the chain was really tight when I removed the sprocket. I don't have the cover off yet but what I can see looks good including the tensioners. If I did replace the timing set it's around $100 for all of it.

Also do you think it will need new pistons or is there a good chance I can go with the ones I have. That #4 piston has a good divet and I worry about the ring gaps being ok-but pistons would add another $100 to the tab. You say I can likely just put it all back together with the new rings, I am assuming that means I don't need to worry about the crank and it's bearings, right? It was a freely revving engine and didn't seem to make excessive noise before and I can't feel any play in the crank-working on it's internals scares me more than anything else.

I don't have an engine stand so I am going to try and do this by popping off the front mounts and hoisting the motor up 2inches and dropping the steering linkage to pull the sump off and access the crank from below.

Again THANKS for your reply I have been asking for help on another Toyota forum and they act like the knowledge they have gained should be doled out in little tid bits or not at all-it's frustrating so I appreciate your input. I will keep you posted on the progress.

 

I would pull the engine completely, dealing with the crank/rods/cap and bearing assy is way easier if the block is "upside down". Just my oppinion though. Pistons should be fine with a decent clean up. I would seriously concider the valves because it looks like #4 exhaust made contact with the piston at some point but that may have been replaced by the previous owner. Dosen't look like it's been making contact recently. Good luck and keep us posted on your progress.

It is awesome how nice and helpful (generally) people are on yotatech. I'm always happy to help someone keep their old girl running, if I happen to have some insight. (not often)

 

I mean you can go as far as you want with it. But I broke a ring, was short on cash so just bought a new set rings, reamed the ridges, honed the cylinders, lapped the valves, put it all back together the same way and it's running fine. I would still consider it a 200+ engine, but hopefully it will run until I can rebuild a 22r bottom end the right way or get a 350 swap together.

Check the crankshaft bearings for copper. They're on their way out if there is any. I had a little on one of mine but went with it anyway. If you go with new then you're probably machining, then you might as well do a full rebuild.

Engine stands are only like 40 bucks new at harbor freight and practically free on craigslist. It's nice to be able to spin and engine around when you're working on it. Difficult would be an understatement to try without it.

Take the valves apart too. Make sure they slide good and aren't too loose in the head. I would just stick with those assuming they all look good.

Also, I use oven cleaner for getting all that carbon off. Or I've heard of putting them in the oven (forget the temp) then spraying them with a water bottle and all the carbon pops off. Take some pictures and let us know what you find.

 

I was hoping that since I was only planning on unbolting the caps and pushing the pistons out the top to replace the rings and hone the bores that it would be less work to leave the engine in-since removing the engine involves many more things to be done. But you're saying that it will be harder to try and do this with it in-Is it because of lack of access or just the tight working space under the truck?

Thanks for the tips on the bearings and removing the carbon. Is there a good way to know if I should stick with STD size rings w/STD size oil ring grooves or go with the ones above with the deep oil ring groove?

Does anyone know how much the engine with transmission weighs? I don't have an engine hoist, just a 3/4ton lever hoist with a reinforced garage ceiling-it has 2x10's spanning the rafters with a steel plate on top and all thread holding a snatch block-do you think that will be sufficient? I am beginning to think I won't be able to do this without a serious upgrade in tools.

 

Update:

I think I know why it suddenly died the other day. While measuring the bores today I noticed that 2,3,4 all have really nice smooth bores with no surface imperfections you can feel, but #1 which was the low blower on the compression test and wet test didn't improve has multiple longitudinal scratches, with the deepest ones opposite the thrust side. Guessing broken rings? The scratches don't seem really severe but you can definitely feel them and feel a difference btwn the cylinders. Will honing be good enough to fix these scratches?

Measured the cylinder bore today:
#1 88.53mm (spec is 88.50 to 88.55) at 10mm from top no more than .01mm difference in any direction, 88.51mm at 60mm down same differences
#2 88.51mm at 10mm, .02mm differences, 88.49mm at 60mm down
#3 same as 2
#4 88.49mm at 10mm, .01mm differences, 88.46mm at 60mm down

Some measurements were below spec (which would seem impossible since the bore must wear some with age and was suppose to be at least 88.5) but the caliper I used has an error of .03mm so I guess you can attribute it to that-it did measure the other things that have known sizes correctly 10mm allen wrench, 40.5mm bolt.

So based on these #'s it looks like I don't need a rebore (unless the broken ring scratches are too much), which would be good because I can't see paying for that anyway-all the shops seem to want as much as recon motor-and I'm guessing new standard rings would be in order since my cylinders are almost as good as new in their dimensions, does this all sound right? Input and opinions appreciated.

 

sounds plenty sufficient for pulling out the motor, prob trans too. Somewhere around 400 pounds for both. Why pulling trans? Don't hone the bores with your crank in there, you'll get grit in your bearings. I've heard of people taping it off with plastic bags and stuff but I don't know if I'd risk it. Your call.

 

The book says you can't pull the motor without either pulling out the trans with it or disconnecting the trans and moving it backwards. It says you can't move the engine far enough forward to clear the primary shaft.

Which do you think would be easier, separating the trans and engine to pull out just the block or just pulling them out together? I am almost thinking about trying to find a w50 (5-speed) at this point, but of course that also means custom trans crossmember...this is going to be one BIG project if it keeps going this way.

Yea I was worried about the grit too, but honestly I am more scared about removing the crank-it makes me think I will end up needing to have it machined and that is crazy pricey for an old motor that it's REALLY hard to find parts for.

 

As long as you keep all the parts in order and put them back just how you found it then it will work just as well as it was working before.

I don't know about older ones, but with my 79 it was easy to pull the engine without pulling the trans. Trans moved plenty to be able to line them up. I also had the radiator out too though.

After you hone it see if your finger nail can catch on it. If it can, it definitely cannot be used, if not I would say it could be used, although a bore job and new pistons is the right way to do it.